The Electron Microscopy (EM) Core is a critical component of the NIDA sponsored addiction center, which provides resources and services contributing to the cellular and subcellular localization of transmitters, receptors and transporters under investigation. These are important for all the basic science research in Projects 1-3, and crucial for the quantitative electron microscopic immunolabeling in Project 3. The core personnel include two faculty members of the Department of Neurology and Neuroscience, Weill Medical College of Cornell University. The Director, Dr. Pickel, has pioneered and established many facets of preembedding EM immunolabeling of a variety of antigens in the central nervous system, and also has substantial expertise in brain anatomy and LM detection of mRNA and proteins under investigation in Projects 1 and 2. The co-director, Dr. Glass has made significant contributions to the use of quantitative morphometric analysis of receptor trafficking under the influence of addictive substances. The resources available in the core include a CM-10 and Techni electron microscopes as well as all smaller equipment seeded for LM and EM structural analysis. The core will provide services and facilities related to (a) characterization of antisera and processing of the tissue for both LM and EM immunolabeling either before (pre-) or after (post-) embedding in resin to for microscopic analysis, (b) in situ hybridization of mRNA on frozen slide-mounted brain sections, (c) image acquisition and quantification of immunolabeling. The Core faculty and resources are located at Weill Medical College of Cornell University, which is across the street from Rockefeller University, and occupies one floor of the Kips Bay building. Access to this facility is easily gained by Rockefeller University associates with the presentation of proper identification. The Goals of the EM Resourse are: 1. To offer state of the art ultrastructural examination of tissues from specific brain region, utilizing standard and novel forms of electron microscopy and other standard imaging techniques, for the Center, including Project 3, possibly Projects 1 and 2, and any pilot projects which require this technology. 2. To develop new technologies for ultrastructural imaging as needed. 3. To train scientists and technical support staff in the various techniques of electron microscopy and related imaging techniques.